The government may own certain rights in the present invention pursuant to NSF Contract No. CHE 8796257.
This invention relates to a series of telomers, polymers and copolymers of the monomer, [1.1.1]propellane, their manufacture, their use, and their manufacture for various applications.
These compounds have unprecedented structures. Due to the presence of bicyclo[1.1.1]pentane rings, they contain up to 14 kcal/mol strain energy per carbon atom. The rigid-rod nature of poly[1.1.1]propellane segments and their tendency to crystallize provide interesting properties.
[1.1.1]propellane is a hydrocarbon compound having the following structure: ##STR1##
This compound will be referred to at various places herein as "(1)" referring to the reference number shown below the structure. Other compounds will be similarly referenced.
Because of the highly strained configuration of this compound at the two bridgehead carbons, [1.1.1]propellane has received much attention in recent years.
Carbon atoms normally have a tetrahedral geometry represented by the following: ##STR2## However, the two bridgehead carbons of [1.1.1]propellane have their geometry inverted such that all four bonds lie on one side of a plane. Thus, the bridgehead carbons of [1.1.1]propellane have the following geometry: ##STR3## As a result of the inverted geometry, [1.1.1]propellane has a very high strain energy.
The first preparation of (1) known to Applicants was described by Wiberg and Walker, 104 J. Am. Chem. Soc. at pp. 5239-5240 (1982), via a reaction of 1,3 dibromobicyclo[1.1.1]pentane with tert-butyllithium in pentane ether. Preparation by this procedure is relatively laborious and yield is low. The article also reports on various properties of (1), and shows reactions of (1) to give 3-methylenecyclobutyl acetate and 3-methylenecyclobutene.
A two step preparation of [1.1.1]propellane from commercially available materials was described by Semmler et al., 107 J. Am. Chem. Soc. at pp. 6410-6411 (1985). The first step involved preparation of 1,1-bis(chloromethyl)-2,2-dibromocyclopropane, and the second step reacted this compound to produce a solution of (1) in pentans/ether. The article also reports on reaction of (1) to a thioether, preserving the bicyclo[1.1.1]pentane ring structure.
Free radical addition to (1) is discussed in Wiberg et al., 27 Tetrahedron Letters, No. 14 at pp. 1553-1556 (1986). It is reported that reaction of (1) with cyanogenbromide gave the 2:1 adduct as the major product, which a significant amount of 3:1 adduct. It is stated that a small amount of 2:1 adduct was observed in the addition of chloroform and carbon tetrachloride to (1).
Applicants have improved the two-step procedure for the preparation of (1), and have also developed a new procedure, wherein e.g. a 5-20 g amount of [1.1.1]propellane at a time can be prepared conveniently. The inventors believe that further scale-up is possible. This development makes this highly unusual compound available as a synthetic starting material.
Applicants' novel synthesis of [1.1.1]propellane in a pentans solution (see Examples 6 and 12 below) provides the advantage of avoiding subjecting the [1.1.1]propellane to the presence of ether. Quite often, when (1) is desired to be used as a starting material to synthesize various compounds in accordance with the present invention, the presence of ether is undesired. For example, reaction of HCOOMe with (1) in the presence of ether produces diethyl ether adducts as the major products, with the desired methyl [n]staffanecarboxylate (see (2d) below) as only a minor product. In contrast, reaction of HCOOMe with [1.1.1]propellane in pentane produces only (2d). As another example, production from (1) of a [2]staffane functionalized at both ends with iodine can not be achieved in the presence of ether. Applicants' method thus provides a [1.1.1]propellane solution free of ether, thereby overcoming the disadvantages experienced by the literature synthesis.
Applicants have also effected radical addition of various reagents across the bridgehead-bridgehead bond in [1.1.1]propellane, leading to several functionalized 1,3-disubstituted bicyclo[1.1.1]pentanes.
In view of the reactivity of [1.1.1]propellane towards radicals, it tends to undergo radical-induced polymerization. Moreover, since an efficient route from (1) to bicyclo[1.1.1]pentane-1,3-dicarboxylic acid has resulted from investigation by the inventors of radical additions to (1) as well, this long-known yet previously poorly accessible diacid is now available via the present invention in large quantities for the synthesis of additional polymers by condensation.